Vif is essential to the replication of primate lentiviruses such as HIV-1 and SIV in vivo. In the last two years,[unreadable] a considerable amount of insight has been gained into the mechanism by which Vif supports viral replication.[unreadable] Vif counteracts the antiviral effects of the cytidine deaminases apobec 3G and 3F. To inhibit viral replication,[unreadable] these cytidine deaminases must be packaged within virions where they edit the minus strand of nascent viral[unreadable] cDNA in the target cell. Vif counteracts the antiviral activity of apobec 3G and 3F by promoting their[unreadable] proteasomal degradation to the extent that there are insufficient levels for packaging into virions.[unreadable] The overall goal of this project is to identify and develop Vif antagonists that can be used to assess the[unreadable] antiviral impact of Vif antagonism in vivo. Project 2 will prioritize Vif antagonists that emerge from the[unreadable] inhibitor screen of Project 1 on the basis of antiviral activity and specificity. Since the most favorable Vif[unreadable] antagonists will be evaluated in the macaque model of SIV pathogenesis and SIV-induced encephalitis,[unreadable] antiviral activity will be evaluated in cells that are relevant to CNS infection namely, primary macrophages.[unreadable] Project 2 will also assess mechanisms of inhibitor escape in vitro and in vivo. The major activities of Project[unreadable] 2 include:[unreadable] Evaluation of antiviral activity and specificity in cells that express apobec (non-permissive cells) and[unreadable] cells that do not express apobec (permissive cells).[unreadable] Evaluation of antiviral activity in CNS-relevant target cells in vitro, namely, primary macrophages.[unreadable] Identification of the mechanism of Vif antagonism by assessing impact of Vif antagonists on virion[unreadable] encapsidation of apobec and on apobec-mediated editing of viral cDNA.[unreadable] Identification of mutations in Vif that confer inhibitor resistance in vitro and in vivo.[unreadable] Collectively, these studies will allow us to identify the most promising lead Vif antagonists and prioritize the[unreadable] selection of inhibitors that will be evaluated in an experimental model of SIV replication and SIV-induced[unreadable] encephalitis in macaques.